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Photoswitching of Dextro/Levo Rotation with Axially Chiral Binaphthyls Linked to an Azobenzene Kazuto Takaishi,*,† Masuki Kawamoto,† Kazunori Tsubaki,‡ and Tatsuo Wada*,† †
Supramolecular Science Laboratory, RIKEN, Hirosawa 2-1, Wako, Saitama 351-0198, Japan, and ‡Graduate School of Life and Environmental Science, Kyoto Prefectural University, Shimogamo Hangi-cho, Sakyo, Kyoto 606-8522, Japan
[email protected];
[email protected] Received May 18, 2009
To examine the reversible photoisomerization and subsequent change of asymmetric field, we synthesized optically active 3,30 -disubstituted-1,10 -binaphthyls with an azobenzene moiety. Reflecting the structural change, the specific rotation and circular dichroism underwent significant variations. Under certain conditions, the positive-negative signals were reversible. Furthermore, the magnitude of these changes showed a 3,30 -substituent dependency. Dibenzyloxy or bis(diphenylmethyloxy) derivatives were better suited for sign interconversion of the optical properties. In contrast, the hydroxy group(s) lacked both optical signals and durability. Axially chiral binaphthyls have a wide, flexible asymmetric field. Hence, they have been extensively used in catalytic asymmetric syntheses,1 specific molecular recognition,2 and helical twisting of liquid crystallines,3 and have (1) (a) Fraile, J. M.; Garcia, J. I.; Mayoral, J. A. Chem. Rev. 2009, 109, 360–417. (b) Yamamoto, H.; Abel, J. P. J. Am. Chem. Soc. 2008, 130, 10521–10523. (c) Rabalakos, C.; Wulff, W. D. J. Am. Chem. Soc. 2008, 130, 13524–13525. (d) Brunel, J. M. Chem. Rev. 2005, 105, 857–898. (2) (a) Ema, T.; Tanida, D.; Hamada, K.; Sakai, T. J. Org. Chem. 2008, 73, 9129–9132. (b) Park, H.; Nandhakumar, R.; Hong, J.; Ham, S.; Chin, J.; Kim, K. M. Chem.;Eur. J. 2008, 14, 9935–9942. (c) Wang, Q.; Chen, X.; Tao, L.; Wang, L.; Xiao, D.; Yu, X.-Q.; Pu, L. J. Org. Chem. 2007, 72, 97–101. (3) (a) Yoshizawa, A.; Kobayashi, K.; Sato, M. Chem. Commun. 2007, 257–259. (b) Akagi, K.; Guo, S.; Mori, T.; Goh, M.; Piao, G.; Kyotan, M. J. Am. Chem. Soc. 2005, 127, 14647–14654. (4) (a) Kamberaj, H.; Low, R. J.; Neal, M. P. Mol. Phys. 2006, 104, 335–357. (b) Kranz, M.; Clark, T.; Schleyer, P. v. R. J. Org. Chem. 1993, 58, 3317–3325.
DOI: 10.1021/jo901030s r 2009 American Chemical Society
Published on Web 06/09/2009
been selected as objects in computational chemistry.4 Moreover, reflecting their chirality, some axially chiral binaphthyls exhibit relatively large optical rotations and circular dichroism (CD).5 The large positive-negative-reversible changes of such optical properties have been evaluated with promising results in the development of novel photoswitching materials. Moreover, optical rotation can be detected at an unabsorbed wavelength, so target compounds do not degrade during measurement. Hence, a switch for dextro (positive)/levo (negative) rotation will lead to the development of noise-cancellation, nondestructive reading of memory devices.6c Although practical recording-reproduction systems have been designed by using optical rotation, practical applications have yet to emerge due to the lack of appropriate compounds.6d,e Irie, Branda, Wang, and Yokoyama et al. have independently reported changes using helicenoids via photochroism,7 but the CD variations are not large or unreported and the change in optical rotations at the sodium D-line, the universal wavelength (589 nm), does not involve a sign inversion. Our research strives to change the CD variations and optical rotations using axially chiral binaphthyl derivatives. We have reported basic compound (R)-1 (Figure 1), which is composed of binaphthyl and azobenzene skeletons.8 Azobenzene skeletons are heavily used photochromic parts,9 and show a significant change in length between the cis and trans forms. The azobenzene moiety of (R)-1 can be reasonably cis-trans photoisomerized. Additionally, isomerization can be detected by the change in CD intensity, which is likely due to the change in the dihedral angle formed by the two naphthalene rings because the dihedral angle is related to the CD intensity. This change is reversible, but the change is small and sign reversal is not detected. Although we have attempted to shorten the linkers so that the structural change of the azobenzene moiety can be more directly transmitted to the binaphthyl, our attempts have been unsuccessful. As an alternative, herein we investigate whether the 3,30 -substituents of the binaphthyl moiety can produce large conformation changes between the cis and trans forms as well as initiate subsequent changes in optical rotation and CD. (5) (a) Minatti, A.; Doetz, K. H. Tetrahedron: Asymmetry 2005, 16, 3256– 3267. (b) Tsubaki, K.; Miura, M.; Morikawa, H.; Tanaka, H.; Kawabata, T.; Furuta, T.; Tanaka, K.; Fuji, K. J. Am. Chem. Soc. 2003, 125, 16200–162001. (c) Higuchi, H.; Ohta, E.; Kawai, H.; Fujiwara, K.; Tsuji, T.; Suzuki, T. J. Org. Chem. 2003, 68, 6605–6610. (6) (a) Murguly, E.; Norsten, T. B.; Brand, N. R. Angew. Chem., Int. Ed. 2001, 40, 1752. (b) Feringa, B. L. Molecular Switches; Wiley-VCH: Weinheim, Germany, 2001. (c) Kawata, Y.; Kawata, S. Chem. Rev. 2000, 100, 1777. (d) Yokoyama, Y.; Ubukata, T.; Saito, M. JP Patent 224834, 2008. (e) Wada, H.; Nishino, K. JP Patent 50317, 2003. (7) (a) Okumura, T.; Tani, Y.; Miyake, K.; Yokoyama, Y. J. Org. Chem. 2007, 72, 1634–1638. (b) Wang, Z. Y.; Todd, E. K.; Meng, X. S.; Gao, J. P. J. Am. Chem. Soc. 2005, 127, 11552–11553. (c) Wigglesworth, T. J.; Sud, D.; Norsten, T. B.; Lekhi, V. S.; Branda, N. R. J. Am. Chem. Soc. 2005, 127, 7272–7273. (d) Irie, M. Chem. Rev. 2000, 100, 1685-1716 and references cited therein. (8) Kawamoto, M.; Aoki, T.; Wada, T. Chem. Commun. 2007, 930–932. (9) (a) Tamaoki, N.; Mathews, M. J. Am. Chem. Soc. 2008, 130, 11409– 11416. (b) Dri, C.; Peters, M. V.; Schwarz, J.; Hecht, S.; Grill, L. Nature Nanotechnol. 2008, 3, 649–653. (c) Muraoka, T.; Kinbara, K.; Aida, T. Nature 2006, 440, 512–515. (d) an Delden, R. A.; Mecca, T.; Rosini, C.; Feringa, B. L. Chem.;Eur. J. 2004, 10, 61–70.
J. Org. Chem. 2009, 74, 5723–5726
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JOC Note
Takaishi et al.
FIGURE 1. (R)-1 and its photoisomerization. SCHEME 1.
Synthetic Route to (R)-4-8a
FIGURE 2. (a, b) CD spectra of (R)-4 and (R)-1. (c, d) Absorption spectra of (R)-4 and (R)-1 (horizontal scales are common). (R)-4 after 365 nm irradiation (blue solid line), (R)-4 after 436 nm irradiation (red solid line), (R)-1 after 365 nm irradiation (blue dotted line), and (R)-1 after 436 nm irradiation (red dotted line). Conditions: 1,4-dioxane (1.0 10-5 M), 20 °C, light path length = 10 mm, irradiation wavelength = 365 nm (10 mW/cm2, 100 s) and 436 nm (10 mW/cm2, 100 s).
a
Conditions: (a) K2CO3, 36%, (b) TiCl4, 91%, (c) RX, base, 35-64%.
As shown in Scheme 1, 3,30 -disubstituted binaphthylazobenzene diads (R)-4-8 were synthesized starting from optically active (R)-2.10 Williamson synthesis of diol (R)-2 and dibromide 3 afforded cyclic compound (R)-4 in 36% yield. Then debenzylation of (R)-4 with titanium tetrachloride for 5 min gave (R)-5 in high yield (91%). Using a higher temperature, longer reaction time, or another Lewis acid (e.g., aluminum trichloride or niobium pentachloride) resulted in an extremely low yield (
